The present invention relates to a method of thinning semiconductor wafers by applying a protection tape to the front of a semiconductor wafer and conducting grinding/etching of the back thereof. The present invention also relates to a back grinding device for grinding the back of a semiconductor wafer with a protection tape attached to the front thereof.
In recent years, thinner semiconductor packages have been in demand. To realize the thinner semiconductor packages, a step of thinning wafers is introduced after completion of a wafer process in a semiconductor assembling operation. In this step, generally, a protection tape is attached to the front of a wafer, and then the back thereof is abraded by grinding.
Further, for the purpose of further thinning the wafers and increasing transverse strength of semiconductor chips by removing a wafer damage layer generated in a grinding process, the back of ground wafers is more and more often subjected to wet etching (hereinafter just referred to as etching).
Generally, when a protection tape is attached to the front of the wafer to grind the back thereof, the size of the protection tape is set to be equal to or larger than the size of the wafer. This is because in the grinding process, by thus setting the size of the protection tape which is disposed between a wafer and a grinding table, the protection tape is allowed to be uniformly present between the wafer and the grinding table. As a result, vibration of the wafer is suppressed and the stable grinding of the back is realized.
In a generally adopted method of attaching the protection tape to the front of the wafer, which is disclosed in Japanese Patent Laid-Open Publication No. HEI 6-310480, a long tape is applied to the front of a wafer, and then the tape is cut along the peripheral edge of the wafer. Another method in practical use is a method of attaching a sheet which has preparatorily been cut to be round to the front of a wafer.
FIGS. 5A–5C are schematic explanatory views showing a method of thinning a wafer in which the front of the wafer is first ground and then etched.
In this thinning method, as shown in FIG. 5A, a protection tape 2 is first applied to the front of a wafer 1, and then a portion of the protection tape 2 protruded from the wafer 1 is cut away along the peripheral edge of the wafer with a cutter 3. Next, as shown in FIG. 5B, the wafer 1 is fixed to a vacuum chuck table 4 for the grinding via the protection tape 2. Then, the vacuum table 4 is rotated, and the back of the wafer 1 is brought into contact with a rotating grinding wheel 5 to conduct grinding. After that, as shown in FIG. 5C, the ground wafer 1 is fixed to a vacuum chuck table 6 for the etching via the protection tape 2. The vacuum chuck table 6 is then rotated, and chemical liquid 7 is applied to the rotating wafer 1 from an upper position to conduct etching of the back of the wafer 1.
However, the conventional thinning method in which the back of wafers are ground and then etched has the following problems. First, in the case where the diameter W of the wafer 1 is smaller than the diameter L of the protection tape 2, as shown in FIGS. 6A and 6B, the chemical liquid 7 tends to be accumulated on the protection tape 2 in an area around the periphery of the wafer 1 during the etching process. Consequently, part 7′ of the accumulated chemical liquid 7 infiltrates toward the front side of the wafer 1, and thereby contaminates the front of the wafer.
On the other hand, in the case where the diameter W of the wafer 1 is equal to the diameter L of the protection tape 2, the peripheral edge of the wafer 1 is etched by chemical liquid 7, which gradually decreases the diameter W of the wafer 1. As a result, the diameter L of the protection tape 2 becomes larger than the diameter W, which generates the same effect as stated above, resulting in contamination of the front of the wafer 1. Therefore, in the case of W≦L, deterioration of quality and reliability of devices is inevitable.